How does the Kaplan-Meier approach to estimating the survival function utilize information from censored observations? a. It does not. All censored observations are dropped from the data sample before the curve is estimated. b. The Kaplan-Meier approach uses the censored observations when considering who is "at risk" of an event at a given time in the follow-up period. All censored observations are considered "at risk" of an event until the time of censoring. c. The Kaplan-Meier approach treats the censoring times as event times. (i.e. it ignores the fact that these observations are censored) d. The Kaplan-Meier approach treats the event times as censoring times